Power electronic module with an improved choke and methods of making same

ABSTRACT

An improved choke assembly for a power electronics device is provided. More specifically, a choke assembly with improved protection from environmental conditions such as dirt and water is provided. An improved choke assembly may include an insulative housing for an inductor coil that seals the inductor coil from the environment.

BACKGROUND

The invention relates generally to the field of power electronic devicessuch as those used in power conversion or for applying power to motorsand other loads. More particularly, the invention relates to devicessuch as motor drives with an improved choke which provides improvedprotection from the environment.

In the field of power electronic devices, a wide range of circuitry isknown and currently available for converting, producing and applyingpower to loads. Depending upon the application, such circuitry mayconvert incoming power from one form to another as needed by the load.In a typical arrangement, for example, constant (or varying) frequencyalternating current power (such as from a utility grid or generator) isconverted to controlled frequency alternating current power to drivemotors, and other loads. In this type of application, the frequency andvoltage of the output power can be regulated to control the speed of themotor or other device. Many other applications exist, however, for powerelectronic circuits that convert alternating current power to directcurrent power, or vice versa, or that otherwise manipulate, filter, ormodify electric signals for powering a load. Circuits of this typegenerally include rectifiers (converters), inverters, and powerconditioning circuits. For example, a motor drive will typically includea rectifier that converts AC voltage to DC. Inverter circuitry thenconverts the DC voltage into an AC voltage of a particular frequencydesired for driving a motor at a particular speed. Often, powerconditioning circuits, such as a choke and/or a bus capacitor are usedto remove unwanted voltage ripple on the internal DC bus. Depending onthe power load, the power conditioning circuits, such as the choke, mayconduct very high levels of current and generate significant levels ofheat.

To dissipate the heat generated by the circuitry of the motor drive, themotor drive unit will typically include a cooling channel that conductscooling air through a heatsink thermally coupled to the semiconductorcircuits described above. To make efficient use of the space within themotor drive unit, the choke is usually deployed within this coolingchannel. Furthermore, the motor drive may be deployed such that thecooling channel is exposed outside of the equipment cabinet. Thus, thechoke may be subject to dust and water.

Therefore, it may be advantageous to provide a motor drive unit with animproved choke that is protected from the environment. In particular, itmay be advantageous to provide a choke with improved protection fromwater and dust.

BRIEF DESCRIPTION

The present invention relates generally to a choke configuration thataddresses such needs. One embodiment of the present invention employs acontainer configured to hold an inductor coil and seal the inductor coilfrom the outside environment, while still allowing the inductor coil tobe disposed about a magnetic core. Although the present invention isdescribed, for convenience, in relation to a motor drive application, itwill be appreciated that chokes fabricated in accordance with presenttechniques may be used in any choke related application, such aselectrical power transmission and telecommunications, for example.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical representation of an exemplary motor drivecircuit employing an improved choke in accordance with one embodiment ofthe present invention;

FIG. 2 is a perspective exploded view of an exemplary motor drive unitemploying an improved choke in accordance with one embodiment of thepresent invention;

FIG. 3 is a perspective view of the improved choke shown in FIG. 2;

FIG. 4 is a perspective exploded view of the improved choke shown inFIG. 2 providing additional details regarding the construction of theimprove choke;

FIG. 5 is a cross section of an exemplary inductor coil shown in FIG. 4providing additional details regarding the construction of the improvedchoke; and

FIG. 6 is a flow chart of an exemplary method of fabricating theimproved choke in accordance with certain embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 is a diagrammatical representation of an exemplary motor drivecircuit 10 employing an improved choke configuration in accordance withpresent embodiments. The motor drive circuit 10 includes a three phasepower source electrically coupled to a set of input terminals 12, 14 and16 that provides three phase AC power of constant frequency to arectifier circuitry 18. In the rectifier circuitry 18, a set of sixdiodes 34 provide full wave rectification of the three phase voltagewaveform. Each input terminal entering the rectifier circuitry 18 iscoupled between two diodes 34 arranged in series, anode to cathode,which span from the high side 38 of the DC bus 36 to the low side 40 ofthe DC bus 36. Also coupled to the DC bus 36 is a choke 20 with improvedtechniques for protection from the environment that will be explainedfurther below. The choke 20 may include inductors 42 that are coupled toeither the high side 38 or the low side 40 of the DC bus 36 and serve tosmooth the rectified DC voltage waveform. Capacitors 44 link the highside 38 of the DC bus 36 with the low side 40 of the DC bus 36 and arealso configured to smooth the rectified DC voltage waveform. Together,the inductors 42 and capacitors 44 serve to remove most of the ACvoltage ripple presented by the rectifier circuitry 18 so that the DCbus 36 carries a waveform closely approximating a true DC voltage. Itshould be noted that the three-phase implementation described herein isnot intended to be limiting, and the invention may be employed onsingle-phase circuitry, as well as on circuitry designed forapplications other than motor drives.

An inverter 24 is coupled to the DC bus 36 and generates a three phaseoutput waveform at a desired frequency for driving a motor 32 connectedto the output terminals 26, 28 and 30. Within the inverter 24, twoswitches 46 are coupled in series, collector to emitter, between thehigh side 38 and low side 40 of the DC bus 36. Three of these switchpairs are then coupled in parallel to the DC bus 36, for a total of sixswitches 46. Each switch 46 is paired with a flyback diode 48 such thatthe collector is coupled to the anode and the emitter is coupled to thecathode. Each of the output terminals 26, 28 and 30 is coupled to one ofthe switch outputs between one of the pairs of switches 46. The drivercircuitry 50 signals the switches 46 to rapidly close and open,resulting in a three phase waveform output across output terminals 26,28 and 30. The driver circuitry 50 is controlled by the controlcircuitry 52, which responds to the remote control and monitoringcircuitry 54 through the network 56.

Turning to FIG. 2, a perspective view of an exemplary motor drive unit58 employing an improved choke configuration in accordance with oneembodiment is shown. Many of the circuit components depicted in FIG. 1,including the choke 20, will typically generate significant amounts ofheat, which can lead to component failure due to overheating. Therefore,the motor control circuit 10 may be packaged within a unit that includesa system for enhancing the heat dissipating properties of the motorcontrol circuit 10. Accordingly, the motor drive unit 58 may include aframe 60 that defines a cooling channel 62 which is thermally coupled tothe electrical components discussed in FIG. 1. The motor drive unit 56also includes a set of fans 64 to provide a flow of cooling air throughthe cooling channel 62. The switches 46, diodes 34, capacitors 44,driver circuitry 50 and controller circuitry 52 are situated adjacent tothe cooling channel 58 on the opposite side of the barrier 66 fromcooling channel. The barrier 66 protects the motor drive circuitry fromexposure to harmful environmental conditions while allowing heat fromthe circuitry to pass through the barrier into the cooling channel. Inthis way, the flow of cool air forced through the cooling channel 62 bythe fans 64 draws heat from the circuitry.

Also included in the motor drive unit 58 is a heat sink 68, which isthermally coupled to the barrier 66 inside the cooling channel 62. Thefans 64 blow cooling air through the heat sink 68, thereby increasingthe transfer of heat from the electrical components to the cooling air.

In some embodiments, the cooling channel may be subject to harshenvironmental conditions. For example, the motor drive unit 58 may bemounted such that the front side of the motor drive unit sits inside acabinet that provides access to the controls and electrical inputs andoutputs of the drive unit 58, while the backside of the motor drive unitsits outside of the cabinet. In this case, although the circuitry on thefront side of the motor drive unit is protected from the environment bythe barrier 66, the cooling channel 62 is exposed to the environment.Additionally, to make efficient use of the space within the coolingchannel, the choke 20 may also be situated within the cooling channel60. Therefore, the choke will be exposed to the environment as well.Therefore, to prevent electrical failure of the choke 20, the choke 20is sealed to provide protection against dust and water, as describedbelow.

Turning to FIG. 3, an exemplary choke 20 that provides improvedprotection from the environment is shown. The choke 20 may include anE-shaped core element 70 coupled to an I-shaped core element 72 withbrackets 74. The two inductor coils 42 are mounted to the outside armsof the E-shaped core element 70. Together the core elements 70 and 72provide for inductive coupling between the inductor coils 42. The levelof coupling may be determined by the spacing between the E-shaped coreelement 70 and the I-shaped core element 72, which may be set by thebrackets 74. Additionally, brackets 74 may also include mounting holes76 for attaching the choke to the motor drive unit 58. The choke 20 mayalso include the high-side bus leads 78 and the low-side bus leads 80,which couple each respective inductor 42 to the high-side 38, or thelow-side 40 of the DC bus 36. As will be described further below withrespect to FIG. 4, the inductor coils 42 are held within a protectivecontainer 82 that seals the inductor coils 42 from the magnetic core andoutside environment. For convenience, the present application describesthe use of an E-I lamination, however, this is not intended to be alimitation of the present invention, and it will be understood thatother embodiments may include any suitable type of lamination shape,such as a U-I lamination, E-E lamination, and C-core lamination, forexample. Furthermore, in some embodiments, the choke 20 may include oneor more than two inductor coils 42. For example, a choke 20 fabricatedin accordance with disclosed techniques may be deployed in a three-phaseinput or output line reactor.

Turning now to FIG. 4, an exploded perspective view of an improved choke20 is shown in accordance with an embodiment. As can be more easily seenin FIG. 4, the E-shaped core element 70 includes a center projection 86and two side projections 88 on which the inductor coils 42 are mounted.The container 82 is open at the top and includes side walls 92, base 94,and center member 96, which projects longitudinally from the base of thecontainer to at least the open top of the container 82, forming a sortof donut-shaped container volume. The container 82 may form a unitarypiece and may be formed from any suitable plastic or othernon-conductive material. In embodiments, the cover 102 is injectionmolded from a polyethylene terephthalate such as Rynite®.

The inductor coils 42 may be formed with any suitable conductor, such asaluminum or copper wire or sheets. In some embodiments, inductor coils42 may be formed by winding the conductor around a bobbin 100.Furthermore, the conductor may be insulated to prevent the loops ofconductor from shorting to each other. The diameter of the inductorcoils 42 and the number of windings of the conductor will, in part,determine the inductance of the choke. The gauge of the wire orthickness of the sheet will determine the power handling. The bobbin 100may be made of any suitable plastic or other non-conductor and may bedimensioned to fit over the center member 96. The high-side bus leads 78and low-side bus leads 80 are electrically coupled to the respectiveends of the inductor coils 42, as will be described further below, withrespect to FIG. 5. The assembled inductor coils 42 are positioned withinthe container 82 around the center member 96.

On top of the container 82 is a cover 102 that seals the inductor coils42 inside the container 82. As with the container 82, the cover 102 maybe formed from any suitable plastic or other non-conductor. Inembodiments, the cover 102 is injection molded from polyethyleneterephthalate. The cover may provide openings 104 which allow the busleads 78 and 80 to pass through the cover 102. In some embodiments, theopenings 104 may be raised cylindrical openings configured to provide apressure seal against the leads 78, 80 and provide a surface overadditional protection may be applied, as will be described furtherbelow, with respect to FIG. 5. In some embodiments, the container 82 maybe filled with a potting material to provide additional environmentalprotection as well as thermal conductivity.

Over the cover 102 is the I-shaped core element 72, which is coupled tothe E-shaped core element 70 via the mounting holes 76. The I-shapedcore element completes the magnetic circuit between the two inductorcoils 42, providing a desired level of mutual inductance between theinductors 42. Furthermore, the mutual inductance may be adjusted bycontrolling the air gap between the E-shaped core element 70 and theI-shaped core element 72. The air gap is controlled by the length of thebracket 74. As with the E-shaped core element, the I-shaped core elementmay include any form of magnetic material, such a ferromagneticmaterial.

Turning now to FIG. 5, a partial cross-section of the assembled inductorcoil 42 of FIG. 4 is shown. As shown in FIG. 5, the bus leads 78 and 80include electrical conductors 108 surrounded by an insulator 110. Thebus leads 78 and 80 project from the container 82 through the raisedcylindrical openings 104, which may be tapered to provide pressureagainst the insulator 110. At the end of the conductor 108 inside thecontainer 82, the insulator 110 is stripped from the conductor 108 andthe conductor 108 is electrically coupled to the inductor coil 42 by anysuitable method, such as soldering, for example. In the embodimentshown, inductor coil lead 114 is crimped and soldered to the conductor108 at the connection point 112. Additionally, where the insulator 110is stripped from the conductor 108, the bus lead may be wrapped withelectrical tape 116 to provide additional protection.

As stated above, the container 82 may be filled with a potting material118, such as an epoxy or other resin, which seals and electricallyinsulates the inductor coil 42 from the outside environment. Because thepotting material 118 is more thermally conductive than air, the pottingmaterial 118 increases the transfer of heat away from the inductor coil42. Moreover, because the container 82 provides mechanical rigidity, thecontainer 82 enables the use of a thin wall of potting material 118,which also serves to increase the transfer of heat away from theinductor coil 42. Increasing the transfer of heat away from the inductorcoil 42 enables the use of a smaller gauge conductor, thereby reducingthe weight, size, and cost of the inductor coil 42. Additionally, thepotting material 118 also reduces the likelihood of electrical failureof the inductor coil 42 by reducing mechanical vibration of the inductorcoil 42.

The potting material 118 also fastens the cover 102 to the container 82.The cover 102 may include a lip 120 that allows the cover 102 to fit orsnap into the container 82, ensuring the proper alignment between thecontainer 82 and the cover 102 and increasing the strength of the sealbetween the container 82 and the cover 102. Additionally, a section ofshrink tubing 122 may be placed around the bus lead 78 at thecylindrical opening 104.

Turning now to FIG. 6, a method of fabricating the choke assemblyillustrated in FIG. 4 is illustrated. Process 124 begins at step 126, inwhich the inductor coil 42 is formed by shaping a conductor into theform of an inductor coil 42. In some embodiments, the conductor may beshaped by winding the conductor around a bobbin 100, however, in otherembodiments, the conductor may be shaped without the use of a bobbin.Next, at step 128, the inductor leads 114 are coupled to the bus leads,i.e. conductor 108. The coupling between the inductor lead 114 and theconductor 108 may be accomplished by any suitable method such assoldering, crimping, and/or the use of mechanical fasteners. Next, atstep 130, the inductor coil 42 is placed inside the container 82. Inembodiments wherein the inductor coil 42 is formed around the bobbin100, the bobbin 100 may be removed from the inductor coil 42 beforebeing placed inside the container 82. Additionally, in some embodiments,the bobbin 100 may remain in place and slide over the projection 96.Next at step 132, the container 82 may optionally be filled with anepoxy, resin, varnish or other potting material. Next, at step 134, thecover 102 is placed over the container 82 before the epoxy cures. Duringthis step, the bus leads 78 and 80 are passed through the openings 104.Next, at step 136, shrink tubing may optionally be positioned around busleads 78 and 80 at the interface between the bus leads 78 and 80 and theopenings 104, and the shrink tubing may be heated to form a seal betweenthe openings 104 and the bus leads 78 and 80. Next, at step 138, theinductor coils 42 inside the containers 94 may be installed over theside projections 88 of the E-shaped core element 70 and the brackets 74.Next, at step 140, the I-shaped core element may be attached to theE-shaped core element 70. The spacing between the I-shaped core element72 and the E-shaped core element 70 may be predetermined according toknown inductive characteristics of such chokes. Finally, at step 142 thechoke assembly may, in some embodiments, be covered with a layer ofvarnish. The varnish may provide an additional level of protectionagainst dust and water, protection against corrosion, and may also serveto securely fasten the inductor coil 42 to the core element 70, therebyminimizing vibrations. The choke 20 may then be installed within themotor drive unit 58.

With the choke arrangement described above, significant protection fromenvironmental conditions can be realized. The cup-and-bobbin stylecontainer seals electrical conductors against water and dust, protectingagainst electrical failure and increasing the overall safety of thedevice. Furthermore, chokes fabricated in accordance with disclosedtechniques are easy to assemble and, therefore, cost effective. Sealingthe container 82 with epoxy provides a double layer of protection anddurability, and also enhances the thermal conductivity of the assembly,allowing heat to pass efficiently from the inductor coil 42 to theoutside environment. Additional features, such as the cylindricalopenings 104 and the shrink tubing 122 provide additional measures ofprotection. By providing a choke with significant protection againstdust and water, the motor drive unit 58 may be mounted such that thecooling channel 62 is exposed to the environment outside of the mountingcabinet.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1-14. (canceled)
 15. A method of fabricating a choke assembly,comprising: preforming a winding of an electrical conductor by windingthe electrical conductor around a bobbin to form an inductor coilconfigured to induce a magnetic field in a magnetic core, two ends ofthe electrical conductor extend externally from the inductor coil;electrically coupling each of the two ends of the electrical conductorto insulated wire leads; placing the inductor coil into a preformedelectrically insulative container comprising an outer sidewall, anintegral base, and an inner sidewall formed by a hollow projection thatextends from the base of the container to at least an open end of thecontainer, the inductor coil surrounding the projection; and inserting amagnetic core through an opening formed by the projection, wherein andthe projection separates the inductor coil from the magnetic core. 16.The method of claim 15, comprising filling the container with a pottingmaterial to encase the inductor coil within the potting material. 17.The method of claim 15, comprising coating the choke assembly withvarnish.
 18. The method of claim 15, comprising coupling each of the twoends of the electrical conductor a respective wire lead, inserting eachof the wire leads through at least one opening in the cover and sealingan interface between the at least one opening and the wire leads. 19.The method of claim 15, wherein the magnetic core comprises two pieces,a first piece being inserted through the opening formed by theprojection, and a second piece being magnetically coupled to the firstpiece after insertion of the first piece through the opening formed bythe projection.
 20. The method of claim 15, wherein the bobbin isinserted into the container and left in the container.
 21. The method ofclaim 15, comprising placing an annular cover over the container,outside dimensions of the cover configured to fit the outer wall of thecontainer and inside dimensions of the cover configured to fit the innersidewall of the container.
 22. A method for fabricating a motor drive,comprising: coupling rectifier circuitry configured to be coupled to anAC power source to inverter circuitry configured to generate drivesignals for driving a motor via a DC bus; coupling a choke assembly tothe DC bus, the choke assembly comprising a bobbin, a preformed inductorcoil wound around the bobbin, a preformed insulative containercomprising an outer wall, an integral base and a hollow projectionextending from the base of the container and creating an internal spacebetween the wall of the container and the projection, the bobbin fittingover the hollow projection and the space configured to receive theinductor coil on the bobbin, the projection forming a passageway throughthe container, an annular cover disposed over the container andconfigured to seal the inductor coil inside the container, and amagnetic core extending through the hollow projection.
 23. The method ofclaim 22, wherein the core comprises an E-shaped magnetic core having acenter projection and two side projections, wherein the container, coiland cover are disposed over one of the side projections, and an I-shapedcore disposed over the annular cover.
 24. The method of claim 22,wherein the container is filled with a potting material to encase theinductor coil within the potting material.
 25. he method of claim 22,wherein the choke assembly is coated with varnish.
 26. The method ofclaim 22, wherein each of two ends of the electrical conductor iscoupled to a respective lead, and the leads extend through at least oneopening in the cover and an interface between the at least one openingand the wire leads is sealed.
 27. The method of claim 22, wherein themagnetic core comprises two pieces, a first piece being inserted throughthe projection, and a second piece being magnetically coupled to thefirst piece after insertion of the first piece through the projection.28. A method for fabricating a motor drive, comprising: couplingrectifier circuitry configured to be coupled to an AC power source toinverter circuitry configured to generate drive signals for driving amotor via a DC bus; coupling two distinct choke assemblies to the DCbus, each choke assembly comprising a bobbin, a preformed inductor coilwound around the bobbin, a preformed insulative container comprising anouter wall, an integral base and a hollow projection extending from thebase of the container and creating an internal space between the wall ofthe container and the projection, the bobbin fitting over the hollowprojection and the space configured to receive the inductor coil on thebobbin, the projection forming a passageway through the container, anannular cover disposed over the container and configured to seal theinductor coil inside the container, and a magnetic core extendingthrough the hollow projection.
 29. The method of claim 28, whereinwithin each choke assembly the core comprises an E-shaped magnetic corehaving a center projection and two side projections, wherein thecontainer, coil and cover are disposed over one of the side projections,and an I-shaped core disposed over the annular cover.
 30. The method ofclaim 28, wherein within each choke assembly the container is filledwith a potting material to encase the inductor coil within the pottingmaterial.
 31. The method of claim 28, wherein the choke assemblies arecoated with varnish.
 32. The method of claim 28, wherein within eachchoke assembly each of two ends of the electrical conductor is coupledto a respective lead, and the leads extend through at least one openingin the cover and an interface between the at least one opening and thewire leads is sealed.
 33. The method of claim 28, wherein within eachchoke assembly the magnetic core comprises two pieces, a first piecebeing inserted through the projection, and a second piece beingmagnetically coupled to the first piece after insertion of the firstpiece through the projection.
 34. The method of claim 28, wherein atleast a portion of the magnetic core is common to the choke assemblies.